Patterns of Disease, Controlled Populations, and Experimental Design

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Abstract
The exponential increase in cardiac coronary disease in mankind in recent decades has been associated with rapid industrialization, improved economics, and increased social and economic competition, as well as with enriched diets. Observations on human populations seem to be inadequate to identify the contribution of any one of these environmental factors to the increased frequency of cardiovascular disease. The environment for mammals and birds in a zoological garden may be less complex and the effects of changing factors upon etiology more readily identified. Thus, coronary disease, with myocardial infarction was 1st seen in mammals and birds in the Philadelphia Zoo during the present decade, and has since become a major cause of death. These animals have received highly constant, high quality diets since 1935. But also within the present decade intra-specific relationships (social environment) were changed as increasing numbers of breeding pairs, or groups, have been assembled and maintained. Thus, among these animals at least, social factors must be assigned a major role in the etiology of coronary disease.